The TLP bonding method has been developed since the 1970s in order to improve the bonding strength of heat resistant super alloys (U.S. Pat. No. 3,678,570). The existing TLP bonding method is carried out in such a manner that an insert material is inserted into between two base metals to be bonded, and then, it is held for a long time at a temperature (i.e., at the bonding temperature), higher than the melting point of the insert material, so that the insert material in liquid phase is isothermally solidified, thereby bonding the two base metals. According to this bonding method, there is almost no distinction between the base metals and the bonding zone thereby improving the bonding strength greatly.
The existing TLP bonding method consists of: a step of melting the insert material, melting the base metals, isothermal solidification, and homogenizing the bonding zone and the base metals. The most important factor affecting the bonding process is the insert material, and there have been many much efforts to develop superior insert materials. The existing bonding method uses insert materials in the form of alloy powders, alloy films and an alloy layer on the bonding surface, which contain lower diffusivity elements and melt at the bonding temperature.
The TLP bonding method (U.S. Pat. No. 4,122,992) developed by Duvall et al, uses a brazing foil and requires a long time (e.g. reportedly up to 100 hours) at a high temperature for the homogenization of the bonding zone and the base metals. This causes a lower productivity, and the deterioration of the base metals.
Meanwhile, the high energy beam method (U.S. Pat. No. 4,691,856) and the boron packing method, in both of which an alloy layer is formed on the bonding surface, involve the problems of forming the alloy layer in a high temperature vacuum or in an inert gas atmosphere.